Question 250081
An aircraft is vertically above a point which is 10km West and 15km North of a control tower.  If the aircraft is 4000m above the ground, how far is it from the control tower?
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s^2 = x^2 + y^2 + z^2 = 100 + 225 + 16
s = sqrt(341)
s =~ 18.466 km